1.
OVERVIEW

This document describes TRACE-P
(TRAnsport and Chemical Evolution over the Pacific), a two-aircraft
mission over the western Pacific to be conducted by the Global
Tropospheric Experiment (GTE) of the National Aeronautics and Space
Administration (NASA) in March-April 2001. TRACE-P is motivated by the
need to better understand how outflow from the Asian continent affects the
composition of the global atmosphere. The mission has two objectives:

to determine the pathways for outflow of chemically and radiatively
important gases and aerosols, and their precursors, from eastern Asia to
the western Pacific;

to determine the chemical evolution of the Asian outflow over the
western Pacific, and understand the ensemble of processes that control
this evolution.

TRACE-P will use two NASA
aircraft, the DC-8 (ceiling 12 km) and the P-3B (ceiling 7 km) operating
out of Yokota Air Force Base (near Tokyo, Japan) and Hong Kong. The
aircraft payloads will include a suite of long-lived greenhouse gases,
photochemical oxidants, aerosols, and their precursors.

TRACE-P is part of a long
series of GTE aircraft missions aimed at better understanding of global
tropospheric chemistry [McNeal et al., 1998]. Over the past two decades,
GTE has conducted missions in several remote regions of the world
(Amazonia, the Arctic, the tropical Atlantic, the Pacific) to characterize
the natural processes determining the composition of the global
troposphere and to assess the degree of human perturbation. The rapid
industrialization now taking place in Asia is of compelling interest.
Energy use in eastern Asia has increased by 5% yr-1 over the past decade
and this rate of increase is expected to continue for the next two decades
[U.S. Dept. of Energy, 1997]. Combustion of fossil fuels is the main
source of energy. Emission of NOx in eastern Asia is expected to increase
almost 5-fold from 1990 to 2020 [van Aardenne et al., 1999]. There is a
unique opportunity to observe the time-dependent atmospheric impact of a
major industrial revolution. Long-term observations of from ground sites
and satellites can provide continuous monitoring of the temporal trend of
atmospheric composition but are limited in terms of spatial coverage
(ground sites) or the suite of species measurable (satellites). Aircraft
missions can complement surface and satellite observations by providing a
detailed investigation of the dynamical and chemical processes affecting
atmospheric composition over broad geographical regions. .

The first objective of TRACE-P
is to identify the major pathways for Asian outflow over the western
Pacific, and to chemically characterize the outflow in a way that provides
a basis for quantitative model analysis. A number of three-dimensional
chemical tracer models have been used in recent years to examine Asian
influence on global atmospheric composition [Berntsen et al., 1996;
Mauzerall et al., 1997; Bey et al., 1999; Carmichael et al., 1998; Jacob
et al., 1999]. TRACE-P will provide the information needed to test these
models. We expect the Asian chemical outflow over the western Pacific to
represent a complicated superimposition of contributions from different
Asian source regions and from long-range transport of European and North
American pollution. The Asian emissions themselves represent a mix of
contributions from fossil fuel combustion, other industrial activities,
biomass burning, vegetation sources, and soil dust. Scavenging of soluble
aerosols and gases during wet convective transport out of the boundary
layer modifies the composition of the outflow. Unusually strong
stratosphere-troposphere exchange around the Japan jet [Austin and
Midgley, 1994] further complicates the interpretation of the outflow by
adding a stratospheric component [Carmichael et al., 1998]. The use of two
aircraft in TRACE-P will allow sampling of a range of Asian outflow
pathways in different regions and at different altitudes, as is needed for
quantitative analysis of the impact of this outflow on global atmospheric
composition.

The second objective of TRACE-P
is to better understand the chemical and dynamical evolution of the Asian
outflow over the west Pacific, focusing on tropospheric O3 and aerosols.
The processes involved in this evolution include photochemistry,
heterogeneous chemistry, gas-to-particle conversion, aerosol growth,
scavenging, and subsidence to the marine boundary layer followed by rapid
removal of some species by deposition. Different patterns of evolution are
expected depending on the direction of outflow (tropics vs. high
latitudes); the altitude (boundary layer vs. free troposphere); the
presence of soil dust, soot, or other chemically active aerosols in the
outflow; and the contributions from natural sources including lightning
and stratospheric intrusions. Previous studies have pointed to the
potential importance of strong UV radiation [Crawford et al., 1997] and
heterogeneous chemistry involving dust aerosols [Dentener et al., 1996] in
modifying the chemical composition of the Asian outflow over the western
Pacific.

The selection of a March-April
flight period for TRACE-P is guided by several factors. Spring is the
season of maximum Asian outflow over the Pacific, due to a combination of
active convection over the continent and strong westerlies [Merrill.
1989]. In summer, deep convection exports Asian air to the upper
troposphere [Kritz et al., 1990; Balkanski et al., 1992] and a significant
fraction of the outflow may travel above the DC-8 ceiling of 12 km. Early
spring also affords the opportunity to sample the biomass burning outflow
from southeast Asia apparent in the Hong Kong ozonesonde data [Liu et al.,
1999] as well as dust outbreaks over central Asia. Photochemistry over the
western Pacific is already active in early spring [Crawford et al., 1998].
Of course, results from a spring mission may not be generalizable to other
seasons because of differences in dynamical and chemical environments as
well as differences in emissions. We expect that sequel missions in other
seasons will be necessary. As discussed in section
3 , a January-February mission would be of particular interest to
isolate the Asian contribution to the outflow from that due to long-range
transport of pollution from Europe and North America.

TRACE-P will build on the
heritage of the previous GTE Pacific Exploratory Missions - West (PEM-West
A and B) conducted over the western Pacific in August-September 1991 and
February-March 1994 [Hoell et al., 1996, 1997]. Key findings of the
PEM-West missions related to the Asian outflow are summarized in
section 2 . The PEM-West
missions were exploratory, with multiple objectives achieved from a single
aircraft. TRACE-P will provide a considerably more extensive
characterization of the Asian outflow to allow for quantitative
interpretation. In addition, TRACE-P will take advantage of numerous
developments in aircraft instrumentation over the past decade including in
particular measurements of HOx, NOx, sulfur, species, aerosols, and UV
actinic fluxes. Ten years will have elapsed between PEM-West A and
TRACE-P, during which Asian emissions will have grown considerably (70%
for NOx; van Aardenne et al. [1999]). Secular change in the composition of
the Asian outflow should be apparent between the PEM-West and TRACE-P
missions.

2.
PRIOR RESULTS FROM THE PEM-WEST MISSIONS

The GTE PEM-West A and B
missions examined the impact of natural and human activities on the
chemistry of the troposphere over the northwestern Pacific Ocean from 10oN
to 50oN. PEM-West A was conducted in August-September 1991 and PEM-West B
in February-March 1994. Important meteorological differences between these
two seasons include the position and strength of the Japan Jet, and the
location of the Pacific High [Merrill et al., 1997]. During
August-September (PEM-West A), the Japan Jet is weaker and shifted north
compared to February-March (PEM-West B). The Pacific High is at its
northernmost and easternmost position during August-September, impeding
continental outflow and enhancing inflow of marine air to the western
Pacific from the south particularly at low altitudes. In PEM-West A, this
southerly flow was accompanied by extensive vertical mixing along a
typhoon storm track oriented parallel to the Asian coast; continental
outflow was largely confined to north of 40oN. PEM-West B experienced
stronger and faster continental outflow over an extended range of
latitudes, principally below 5 km due to weak convection over eastern Asia
in winter. Blake et al. [1997] found higher mixing ratios of continental
hydrocarbons and halocarbons during PEM-West B than A, especially at low
altitudes, and similar observations were made for acidic gases [Talbot et
al., 1997]. The composition of the hydrocarbon mix indicated a more recent
origin for the continental outflow in PEM-West B.

The strong Asian outflow
during PEM-West B had a major influence on the regional ozone budget over
the western Pacific. Photochemical model calculations by Crawford et al.
[1998] showed net ozone production taking place at all altitudes, in
contrast to PEM-West A where net loss at low altitudes balanced net
production at higher altitudes. PEM-West B marked the first time that net
ozone production has been found to take place in the lower marine
troposphere. That this condition was observed in late winter/early spring
further emphasizes the critical role of fast transport of ozone precursors
from the Asian continent. Calculated rates of increase in the tropospheric
ozone column during PEM-West B were as large as 2% per day south of 30oN
and 1% per day to the north. An important implication of the rapid
transport observed during PEM-West B is that the photochemical activity of
the continental outflow remained strong even after several days of travel
time over the ocean.

3.
METEOROLOGICAL SETTING FOR TRACE-P

The first 2-3 months of the
year come under the influence of the winter monsoon in east Asia,
characterized by intense Siberian high pressure systems and strong outflow
over the western Pacific, with maximum sea level pressures occurring in
December-February [Yihui, 1994]. The percentage of days when the high
pressure exceeds 1050 hPa is as follows: November (25), December (45),
January (51), February (38), March (13), and April (3) [Yihui, 1994].
During the peak of the monsoon in December-February there is strong
subsidence in the major part of the east Asian continent, pollution is
trapped in the boundary layer, the middle free troposphere is often
cloudless in association with the high pressure systems and rainfall is
practically non-existent (Figure
1 ). Sandstorms have maxima in Kantze (30oN, 103oE) in
December-February and in Hami (43oN, 93oE) in March-May [Watts, 1969].
They depend on the occurrence of strong winds and the absence of snow.
Precipitation is very low over China in January but is substantial over
Japan. As the year progresses the precipitation belt moves westward
towards the coast, gradually increasing until it covers the entire area of
interest by May.

Another feature of these high
pressure systems is the occurrence of cold air outbreaks. Some of these
outbreaks, which themselves will contain pollution trapped in layers by
subsidence, bring cold air into southern China and sweep pollution
southwards over the South China Sea. The fact that the Siberian
anticyclone dominates the circulation in December-February implies that
much of the pollution originating in continental east Asia will flow
clockwise out to sea then return to the southwest and move southwards into
the South China Sea. Some pollution injected at higher altitudes within
the continent may be caught in the westerlies and head directly out to
sea. This domination by the anticyclonic subsidence keeps local pollution
at low altitudes permitting pollution entering China's airspace from the
west to be partly distinguished from that which originates in China. If
measurements are made off the coast, it is not correct to attribute this
pollution measured solely to China. Even the pollution that heads
southward over the South China Sea, as noted above, is likely to be
substantially oxidized in its passage towards the ITCZ (at about 10oS in
the previous PEM-West B mission). After pollution has being raised in the
ITCZ there is a flow back towards China (at 200 hPa) before the air turns
eastwards and moves into the westerly wind global circulation [Newell et
al., 1997]. Hence the impact of pollution from China itself on the global
atmosphere is not easy to measure.

Figure 1. Monthly mean precipitation,
January-March

In the upper troposphere the
main meteorological feature is the westerly jet stream with
December-February mean speeds of 65 ms-1 south of Japan [Newell et al.,
1972]. This phenomenon brings pollution from further west as will be
illustrated later. As convection starts in late March pollution from China
itself is mixed with the pollution arriving from the west from other
longitudes before it can be measured offshore. Instabilities in the jet
stream are often associated with the transfer of air from the stratosphere
to the troposphere, and these form another major factor influencing the
chemistry of the region.

Figure 2. Climatological flow
streamlines

Mean streamlines for
January-April 1997 are shown in Figure
2 for levels of 1000, 850, 700, 500, 300 and 200 hPa. In January the
clockwise flow at 1000 and 850 hPa associated with the continental
anticyclone carries boundary layer air out over the ocean north of Taiwan
and then back westwards over the South China sea, the Philippines and the
region north of New Guinea. At 700 hPa the flow moves eastwards from the
continent in the 20-50oN region. There is some recirculation back towards
the west south of 15oN around the subtropical anticyclone. This provides
more opportunity to measure the chemical evolution of pollution. At 300
hPa winds reach 70 m s-1 near Japan, as in the climatology, yielding a
transit time of only a few days between Asia and North America. The
maximum speeds diminish to 48 m s-1 and 31 m s-1 by March and April
respectively. The flow pattern is quite similar in February, although in
the 10-year precipitation climatology (1988-1998) there is some
precipitation along the coast, east of Hong Kong and south of Shanghai (Figure
1 ).

By March the flow is onshore
at 1000 hPa and 850 hPa for China south of about 30oN but is still
offshore further north and in the upper troposphere. The lower layer
continental anticyclone is much weaker by March and disappears by April.

The differences between
sampling in the January-February period and sampling in the March-April
period can be illustrated by trajectories. Three sets for January and
March are shown in Figure 3
. The first set originates from 5 polluted regions of China with one
trajectory per day starting at 7 points near each city for the days 1-26,
1997, of each indicated month. The color changes along the trajectory
indicates the changes in pressure of the trajectory. Trajectories are
divided into two groups depending on the pressure at the end, after five
days, being > or < 700 hPa. As expected from the wind maps and
analysis of PEM-West B data [Newell et al., 1997] considerable low-level
flow heads to the south in January, some reaching the SPCZ after a period
greater than 5 days. In March most of the air heads out eastwards and a
significant fraction ends in the upper troposphere.

The second set shows air
parcels arriving at a wall along 100oE at 20-40oN in western China. Seven
pressure levels were used with 41 points spaced along each pressure level.
Monthly dates 17-22 were used for the calculation for each month shown.
Pressure levels are shown at the beginning of each 5 day trajectory to the
wall. In both months it seems that more of the air parcels arrive at the
wall from the upper troposphere than from the lower troposphere. In
January air arrives from central Africa, north Africa, even the north of
Greenland and the west of the United States. The flow converges laterally
in the upper troposphere from two main streams and one subsidiary stream.
In the lower troposphere there are two main source regions: the Middle
East and Europe. In March 1997 the sources are not so distant from the
wall because of the lower speeds and do not span quite such a large range
of latitude.

Figure 3. Air flow trajectories

The third set shows forward
trajectories for air leaving the same wall. The spread in latitude is
again large in January in the upper troposphere, with two main plumes. The
spread into the tropics is minimal but there is an extensive spread to
higher latitudes in January. On the contrary there is a downstream
convergence in the lower troposphere towards the central Pacific in both
months. Again little air moves south of the southern boundary of the wall
at 20oN. Thus assuming the arriving wall air and the surface layer derived
air are combined when sampled, it seems that in January they could be
identified because much of the former head to the south (as we suggested
in the discussion of the winter anticyclones). On the other hand, sorting
the local and distant sources in March would seem to be practically
impossible as they will be well mixed. There are very few if any days of
continental anticyclonic flow in April hence the possibility of
differentiating sources is very low.

In summary then there are two
possible approaches:

Fly in the same period
as in PEM-West B (January 25-March 16, 1994) and concentrate on studies
of the chemical evolution of pollution off the coast and to the south of
China. This would have the advantage that changes which have occurred
over the past decade could be studied.

Study outflow at
various longitudes across the Pacific and monitor the evolution of
pollution which would be essentially derived from the Euro-Asian
continent and even North America. That would have to be done before the
onset of major monsoon rains so sampling could start in the beginning of
March. Flights from Hong Kong northwards along the coast and from Tokyo
southwards and Guam northwards would be appropriate.

4.
FLIGHT PLAN

Nominal flight tracks for the
two TRACE-P aircraft are shown in Figure
4 . The aircraft will operate out of two sites: Yokota Air Force
Base (near Tokyo, Japan) and Hong Kong. As shown in
Figure 4 , these two bases
of operations are well situated to sample Asian outflow over the full
range of latitudes from 10oN to 50oN. Specific targets for the flights out
of Hong Kong will include biomass burning pollution from southeast Asia
[Liu et al., 1999], tropical inflow and outflow, and industrial outflow
from the Pearl River Delta inland of Hong Kong which is one of China's
fastest growing regions. Specific targets for the flights out of Yokota
AFB will include outflow of pollution from northern China. Korea, and
Japan [Akimoto and Narita, 1994; Carmichael et al., 1998], long-range
transport of European and North American pollution in the westerlies, dust
outbreaks, and stratospheric influence combined with continental outflow
in the Japan jet [Wakamatsu et al., 1989; Murao et al., 1990; Austin and
Midgley, 1994; Carmichael et al., 1998].

The sampling of outflow in
flights from Yokota AFB and Hong Kong will use a wall pattern (Figure
5 ) with the aircraft flying stacked patterns of horizontal legs
perpendicular to the outflow and separated by a few km altitude. Regions
of outflow will be identified on a day-to-day basis using meteorological
and chemical tracer model forecasts. The length of a typical wall will be
several hundred km, and the wall pattern may be repeated over the duration
of the flight, in order to assess photochemical aging of reactive species
as part of our process studies and also to obtain the representative
sampling of the outflow needed for testing 3-dimensional chemical tracer
models. The two aircraft will be used to sample different ouflow regions
on any particular day; typically the P-3B will focus on low altitudes and
the DC-8 on high altitudes. Since outflow at different altitudes may be
geographically and temporally separated, the DC-8 and the P-3B will in
general cover different horizontal flight tracks and may not fly on the
same days or out of the same operational base.

Figure 4. Nominal TRACE-P flight
tracks.

Chemical aging of the Asian
outflow over the western Pacific will be examined with flights extending
east from Hong Kong and Yokota AFB, and most specifically with DC-8
flights using Guam as an overnight stop (Figure
4 ). These flights will sample Asian outflow having traveled a few
days over the western Pacific. Under conditions of steady westerly
outflow, transects between Yokota AFB and Guam may be used to revisit air
previously sampled close to the China coast on flights south of Yokota AFB
or north of Hong Kong (Figure 4
). A generic pattern for the chemical aging flights is shown in
Figure 6 . Specific patterns
will be guided by meteorological and chemical forecasts in the field.
Near-Lagrangian sampling will be attempted if meteorological conditions
are favorable.

Figure 5. Typical wall flight patterns
for the DC-8 and P-3B in TRACE-P

It is expected that 160 and
171 flight hours will be allocated to the DC-8 and P-3B aircraft
respectively for this mission, including test and transit flights. More
hours will be allocated for the P-3B to account for the longer transit
time to the study region. Sorties out of Hong Kong and Yokota AFB will
include both 8-hour and 10-hour flights. A nominal breakdown of flight
hours is shown in Table 1 .
The DC-8 will conduct 4 sorties out of Hong Kong and 7 out of Yokota AFB,
while the P-3B will conduct 4 sorties out of Hong Kong and 6 out of Yokota
AFB. The DC-8 sorties will include one return flight to Guam (to be
counted as two sorties).

5.
MEASUREMENT PRIORITIES ABOARD THE AIRCRAFT

Priority measurements for the
DC-8 and the P-3B are listed in Table 2. The priorities reflect the focus
of the mission on radiatively important species, photochemical oxidants,
sulfur, and aerosols. Chemical tracers of air masses are also included in
the list. The priority ratings 1-4 in Table 2 indicate a decreasing level
of importance of the measurement for meeting the mission objectives.
Priority 1 measurements are of highest importance and a failure of one of
these measurements prior to the mission or in the field could alter
mission plans. It is expected that the aircraft will include all
measurements of priority 1 and 2 plus some measurements of priority 3.
Measurements of priority 5 ("new-technology") would enhance the
mission but are considered not yet technically established in terms of
airborne sampling. It is expected that at least one such instrument will
be included in the payload.

The instrument detection
limits and time resolutions quoted in Table 2 are minimum requirements
below which the instrument will be considered not responsive to the
objectives of the mission. Performance beyond these minimum requirements
in terms of speed, precision, accuracy, and specificity will be an
important consideration in the selection of the aircraft payload. The size
of instrumentation will also be an important consideration.

Table 2.a Measurement
requirements for the DC-8 instrumentation

Species/Parameter

Priority

Detection Limit

Time Resolution

Time Resolution

O3 (in situ)

1*

3 ppbv

30 sec

5 sec

NO

1

3 pptv

1 min

10 sec

H2O

1*

3 ppmv

1 min

10 sec

CO

1*

5 ppbv

1 sec

10 sec

meteorological
parameters

1

aircraft standard

1 sec

1 sec

remote ozone

1

5 ppbv

Z<500 m

Z<500 m

remote aerosol

2

scattering ratio .02

Z<60 m

Z<60 m

remote H2O

2

0.01g/kg

Z< 500m

Z< 500m

PAN

2

5 pptv

5 min

5 min

HNO3

2

5 pptv

5 min

2 min

H2O2

2

10 pptv

5 min

5 min

CH3OOH

2

10 pptv

5 min

5 min

speciated hydrocarbons

2

20 pptC

5 min

5 min

halocarbons

2

2 pptv

5 min

5 min

OH

2

1x 105 molec/cm3

5 min

5 min

HO2

2

1x107 molec/cm3

5 min

2 min

NO2

2

5 pptv

1 min

1 min

CO2

2

0.5 ppmv

1 min

1 min

N2O

2

0.5 ppbv

1 min

1 min

CH4

2

20 ppbv

1 min

1 min

acetone

2

50 pptv

5 min

5 min

spectrally resolved
actinic fluxes

2

0.1 mw/nm/cm-2

30 sec

30 sec

J(O1D)

2

2 X 10 -6 /s

30 sec

30 sec

J(NO2) (+)

2

1 X 10-4/s

30 sec

30 sec

UV Radiometer (+)

2

1 watt/m2

10 sec

10sec

SO2

2

5 pptv

5 min

5 min

Storm Scope

2

range 400 km

<3 min hold time

NA

CH2O

2

50 pptv

5 min

1 min

Aerosols size
distribution

2

10 nm - 2.0 mm

10 sec

10 sec

Aerosol composition

2

5 pptv

10 min

10 min

remote temperature

2

2 K

1 km

Black
carbon/aethelometer

3

0.1 mg/m3

5 min

5 min

Nephelometer

3

Organic nitrates

3

6 pptv

5 min

5 min

Ultra fine aerosols

3

size range 3-15

5 min

5 min

DMS

3

1pptv

5 min

5 min

H2SO4 (g)

3

2 x 105 molec/m3

5 min

5 min

NH3

5

10 pptv

5 min

2 min

Alcohols

3

20 pptv

5 min

5 min

organic acids

3

10 pptv

5 min

5 min

22Rn

3

0.05 Bq/SCM

5 min

5 min

210Pb

3

0.1 Bq/SCM

10 min

10 min

7 Be

3

1.0 Bq/SCM

10 min

10 min

MSA(g)

4

2 x 10 5

1 min

10 sec

DMSO(g)

4

2 x 10 6

1 min

10 sec

ICN

4

CCN

4

HNO4

5

5 pptv

5 min

5 min

RO2

5

0.1 pptv

5 min

5 min

>C1 - Aldehydes

5

20 pptv

5 min

5 min

>C3 - ketones

5

20 pptv

5 min

5 min

real-time hydrocarbons

5

2 pptv

1 min (real time)

1 min (real time)

Size-resolved single
particle composition

5

Species-dependent

<1 min

1 sec

remote chemical
species

5

species dependent

5 min

1 min

Table 2.b Measurement
requirements for the P-3B instrumentation

Species/Parameter

Priority

Detection Limit

Time Resolution

Time Resolution

O3 (in situ)

1*

3 ppbv

30 sec

5 sec

NO

1

3 pptv

1 min

10 sec

H2O (+)

1*

3 ppmv

1 min

10 sec

CO

1*

5 ppbv

1 sec

10 sec

meteorological
parameters

1

aircraft standard

1 sec

1 sec

vertical winds (+)

2

10 hz

10 hz

PAN

2

5 pptv

5 min

5 min

HNO3

2

5 pptv

5 min

2 min

H2O2

2

10 pptv

5 min

5 min

CH3OOH

2

10 pptv

5 min

5 min

speciated hydrocarbons

2

20 pptC

5 min

5 min

halocarbons

2

2 pptv

5 min

5 min

OH

2

1x 105 molec/cm3

5 min

5 min

HO2

2

1x107 molec/cm3

5 min

2 min

NO2

2

5 pptv

1 min

1 min

spectrally resolved
actinic fluxes

2

0.1 mw/nm/cm-2

30 sec

30 sec

J(NO2) (+)

2

1 x 10-4/s

30 sec

30 sec

UV Radiometer (+)

2

1 watt/m2

10 sec

10sec

CO2

2

0.5 ppmv

1 min

1 min

N2O

2

0.5 ppbv

1 min

1 min

CH4

2

20 ppbv

1 min

1 min

SO2

2

5 pptv

5 min

5 min

CH2O

2

50 pptv

5 min

1 min

Aerosol size
distribution

2

10 nm - 20 mm

5 min/per scan

5 min/per scan

Ultra fine aerosols

2

size range 3-10

1 min

1 min

Condensation nuclei

2

10/cm3

10 sec

10 sec

Aerosol composition

2

5 pptv

10 min

10 min

H2SO4 (g)

2

2 x 105 molec/m3

5 min

5 min

Storm Scope

2

range 400 km

<3 min hold time

NA

DMS

3

1pptv

5 min

5 min

acetone

3

50 pptv

10 min

10 min

Black carbon
/aethalometer

3

0.1 mg/m3

5 min

5 min

Nephelometer

3

10-7/m3

10 sec

10 sec

Alcohols

3

20 pptv

5 min

5 min

Organic nitrates

3

6 pptv

30 min

10 min

remote aerosol

3

scattering ratio .02

Z<60 m

Z<60 m

organic acids

3

10 pptv

10 min

10 min

NH3

3

10 pptv

5 min

2 min

MSA(g)

4

2 x 10 5

1 min

10 sec

DMSO(g)

4

2 x 10 6

1 min

10 sec

ICN

4

0.1 cm-1

1 min

1 min

CCN

4

1 cm-1

1 min

1 min

real-time hydrocarbons

5

2 pptv

1 min (real time)

1 min (real time)

HNO4

5

5 pptv

5 min

5 min

RO2

5

0.1 pptv

5 min

5 min

>C1 - Aldehydes

5

20 pptv

5 min

5 min

>C3 - ketones

5

20 pptv

5 min

5 min

Size-resolved single
particle composition

5

Species-dependent

<1 min

1 sec

remote chemical
species

5

species dependent

10 min

1 min

Table 2.c Priority
descriptions

Priority

Description

Meaning

1*

Mission Critical

The measurement is
essential for the interpretation of data related to several objectives
of the mission

2

Very Important

The measurement is
important for several objectives of the mission

3

Important

The measurement is
important for some aspects of the mission

4

Less Important

The measurement could
be useful but information not considered critical..

5

New Technology

The measurement
represents the application of new airborne technology.

* redundancy will be provided
where feasible.

+ will be provided by the GTE
Project Office

6.
SUPPORTING MEASUREMENTS AND ANALYSES

Supporting measurements for
TRACE-P are intended to place the aircraft observations in a broader
temporal and spatial framework. Ozonesondes have proven to be particularly
valuable for that purpose in past GTE missions. TRACE-P will include a
program of intensified launches at three established ozonesonde sites:
Hong Kong [Chan et al., 1998], a southern Japan island site such as Naha,
and a Japan mainland site such as Tateno. Ozonesondes will be launched
once a week from March 2000 to March 2002 (one year before to one year
after the mission) and twice a week during the mission.

Measurements at coastal sites,
islands (Cheju, Lanyu, Oki...), and ships will also be important for
extending the aircraft observations in TRACE-P. Key species to be measured
include ozone, aerosols, CO, and hydrocarbons. It is expected in the
framework of APARE that the Asian partners to NASA will play a leading
role in the operation of these surface measurements.

Space-based observations from
the Measurement Of Pollution In The Troposphere (MOPPITT) and the Global
Ozone Monitoring Experiment (GOME) instruments should be of considerable
value for interpretation of the TRACE-P data. MOPPITT (to be launched in
polar orbit in summer 1999) will provide global distributions of CO
vertical profiles including 4 levels in the troposphere. GOME (in polar
orbit since 1995) is expected to provide operational data for tropospheric
ozone columns by the time of the TRACE-P mission.

Day-to-day flight planning in
the field will require high-quality meteorological forecasts and
back-trajectory analyses. Chemical and aerosol forecasts using 3-D model
simulations with forecast weather would be of considerable value for
guiding the aircraft towards outflow regions and for planning chemical
aging flights. These 3-D models can provide an integrated analysis of the
outflow from the Asian continent that includes the effects of emissions,
boundary layer dynamics and chemistry, convective pumping, and long-range
transport from Europe and North America. Both mesoscale and global models
should be engaged in this role. Considering that a major goal of TRACE-P
is to provide the observations needed for testing the simulation of Asian
outflow in 3-D chemical tracer models, use of these models in the flight
planning stage both before and during the mission is of great importance.
Additional modeling support will be needed in the field for quick analysis
of the aircraft observations using a combination of statistical
approaches, 0-D photochemical box models, and aerosol models. This
modeling support is of great value for monitoring the achievement of the
mission objectives and for guiding flight planning.

7.
LINKS TO OTHER AIRCRAFT PROGRAMS

Itis expected that the Aerosol
Characterization Experiment - Asia (ACE-Asia) aircraft mission will be in
the field concurrently with TRACE-P (B.J. Huebert is the ACE-Asia mission
scientist). ACE-Asia will study the outflow of aerosols and aerosol
precursors from Eastern Asia to the Pacific. Its objectives are to
characterize the physical, chemical, and radiative properties of Asian
aerosols that impact the Pacific atmosphere and to quantify the processes
needed to model these properties. ACE-Asia will involve two years of
observations from a surface network, in addition to springtime intensive
observations with aircraft and ships in 2000 and 2001. Since the goals of
TRACE-P and ACE-Asia are complementary, collaboration will take place to
the extent possible while maintaining the integrity and independence of
each mission. The collaboration may take several forms: allocating a
fraction of the P-3B payload to aerosol-related measurements, reciprocal
representation at planning meetings, conducting joint flight operations,
and sharing some portion of the infrastructure support when the aircraft
are operating from common airfields.

There are tentative plans to
conduct an APARE/BIBLE aircraft campaign in 2001 in complement of TRACE-P
(Y. Kondo is the BIBLE mission scientist). Previous BIBLE campaigns using
a Japanese Gulfstream 2 aircraft have investigated Asian outflow and
biomass burning in southeast Asia in different seasons. The most effective
use of a BIBLE mission in support of TRACE-P would be to extend the
temporal range of TRACE-P with flights in other seasons.

The recently conducted
Photochemical Ozone Budget of the Eastern North Pacific Atmosphere
(PHOBEA) aircraft campaign off the northwest coast of the United States in
April-May 1999 (http://weber.u.washington.edu/~djaffe/phobea/) revealed
layers of high ozone and aerosols transported across the north Pacific
from the Asian continent (D. Jaffe is the PHOBEA mission scientist). A
second PHOBEA mission conducted concurrently with TRACE-P would be of
great value for investigating the long-range transport and chemical
evolution of the Asian outflow sampled with the TRACE-P aircraft.

Blake, N.J., et al.,
Distribution and seasonality of selected hydrocarbons and halocarbons over
the western over the western Pacific basin during wintertime, J. Geophys.
Res., 102, 28,315-28,333, 1997.

Crawford, J., et al., An
assessment of ozone photochemistry in the in the extratropical western
North Pacific: Impact of continental outflow during the late winter/early
spring. J. Geophys. Res., 102, 28,469-28,488, 1997.